Question

what do these two changes have in common?
milk going sour
newly poured concrete becoming hard
select all that apply.
both are caused by heating.
both are changes of state.
both conserve mass.
both are chemical changes.

Explanation:

1. Analyze "Both are caused by heating": Milk souring is due to microbial action, concrete hardening is a hydration reaction, not mainly heating - so this is incorrect.
2. Analyze "Both are changes of state": State change (like solid - liquid - gas) doesn't apply here; these are chemical changes - so this is incorrect.
3. Analyze "Both conserve mass": According to the law of conservation of mass, in any chemical or physical change, mass is conserved. Both milk souring (chemical) and concrete hardening (chemical) follow this - so this is correct.
4. Analyze "Both are chemical changes": Milk souring involves microbial fermentation (new substances), concrete hardening involves hydration (new compounds like calcium silicate hydrates) - both are chemical changes - so this is correct.

Answer:

• Both conserve mass.
• Both are chemical changes.